The present exemplary embodiments generally relate to multi-layered composite structures and find particular application in connection with systems and methods for the production of multi-layered integral vasculature networks incorporated within such structures, and will be described with particular reference thereto. It is to be understood, however, that it also finds application in other usage scenarios, and is not necessarily limited to the aforementioned exemplary embodiment.
Fiber-reinforced composites are widely and increasingly used in military and commercial systems alike for their light weight and easily tailored structural properties. For example, in a Boeing 787, more than 50% of the aircraft is composites by weight, and composite laminates makeup almost all the exposed areas of the aircraft. Though variations exist, carbon-fiber composites are generally constructed by laying down many layers of carbon fiber pre-preg or pre-impregnated carbon fiber sheets employing various fiber orientations for mechanical property control. Pre-preg or pre-impregnated layers are alternated with layers of epoxy and in some cases honeycomb or foam; these are stacked on a 3D mold and then cured.
Unfortunately, these structures are not damage-tolerant and introduce severe thermal management challenges when combined with increasing levels of electrical actuation and control. Integrated vasculature networks allow straightforward solutions to both of these challenges by allowing integration of cooling networks into wing surfaces or delivery of self-healing compounds, among other uses. Such a network, for example, might need to distribute fluid throughout multiple layers of the structure without increasing weight and decreasing strength. Further, adding a vasculature channel network to a large area composite structure has numerous applications, such as enhanced thermal management, enhanced signature control, adaptive camouflage and erosion damage repair, among other uses. Ideally, the process to fabricate the vasculature network also would be fully compatible with existing composite tooling to enable simple process integration while adding this new advanced functionality.
There have been several attempts to introduce a vasculature network into existing composite structures. In one attempt, tubes were inserted into a foam core/epoxy-glass laminate structure yielding a low impact on strength; however, a significant weight increase of almost 30% was observed. In another attempt, a sacrificial polylactide (PLA) polymer weave was utilized to fabricate microchannels. However, this method was unable to lay down channels with significant feature scales and interweaving these channels with the fiber reinforcement complicated the fiber design and necessitated compromises in optimal mechanical strength. A number of printed options have also been explored including an effort to print a fugitive ink matrix of interpenetrating fluid networks. Although this methodology enabled a range of features sizes, this 3D printing technology lacks the ability to translate to large areas.
These unsatisfactory realizations of vasculature are far from what is required for useful application. Beyond the aforementioned requirements, for a thermal management or erosion control application, the vasculature network must be able to deliver fluid across as much of the surface area as possible. Fabrication must be both repeatable and reliable—the same network must exist in all units and be free of defects that may block fluid flow. The network must also have a tight feature density, span multiple length scales and be easily adapted to the complexity of a large area in order to optimize the vasculature network not only for functionality, but power and weight requirements of any supporting systems. For example, the skin of an aircraft wing contains significant numbers of fasteners, mating features and connectors that would require a large variety of vasculature structures to achieve optimal fluid distribution. A simple repetitive vasculature structure that does not route the fluid around these structures in an intelligent way will have inferior performance.
The best existing methods for creating vasculature give structures that are both weaker and heavier and are also completely incompatible with fiber-reinforced composite layup manufacturing processes.
The present exemplary embodiments provide new systems and methods which overcome the above-referenced problems and others.